Safes and similar security structures

ABSTRACT

A slab or panel for use in a safe or similar structure comprises a layer of material resistant to drilling and other forms of mechanical attack backed by a layer of material, preferably graphite, which melts and vaporizes but does not substantially react exothermically with oxygen at the temperatures generated by a thermic lance, i.e., of the order of 3,000* C. The melting and vaporization involves the provision of such large amounts of latent heat thus taking several times as long to burn a hole through the slab. The material for resisting mechanical attack preferably comprises nuggets of heard material in a ductile metal matrix and a convenient form of construction there is a single layer of this material and a single layer of the vaporizable material. The vaporizable material is preferably in the form of blocks of triangular section fitted into compartments defined by metallic spacing members supported between a pair of steel plates.

OR 3 .9 6 4 5 9 2 l 6 Unite States Patent 3,645,21 6 Redford et al. Feb.29, 1972 [54] SAFES AND SIMILAR SECURITY 3,122,883 3/1964 Terner..l6l/213 STRUCTURES 3,334,040 8/1967 Conrad ..l6l/213 [72] inventors:Arthur S. Redford, Wolverhampton; Primary Examiner Reinaldo Machado 33:?Oakengms, 10th 0f Attorney-Holcombe, Wetherill & Bisebois [73] Assignee:Chubb & Sons Lock and Sale Company [57] ABSTRACT Limited, Wolverhampton,Staffordshire, England A slab or panel for use in a safe or s milarstructure comprises a layer of material resistant to drilling and otherforms of [22] Filed: Jan. 29, 1970 mechanical attack backed by a layerof material, preferably graphite, which melts and vaporizes but does notsubstantially [2H Appl' 6758 react exothermically with oxygen at thetemperatures generated by a thermic lance, i.e., of the order of 3,000C. [30] Foreign Appncaflon priority Dam The melting and vaporizationinvolves the provision of such 3 large amounts of latent heat thustaking several times as long Feb. 3, 1969 Great Britain ..5,728/69 tobum a hole through the slab, The material for resisting mechanicalattack preferably comprises nuggets of heard [52] U.S.Cl ..l09/82material in a ductile metal matrix and a convenient form of [51] Int. Cl..E05g 1/02 st cti there is a si gle aye of this material and a single[58] Field of Se h 109/80, 81, 82, 33, 84, 24, layer of the vaporizablematerial. The vaporizable material is 109/29; 1 2 3 preferably in theform of blocks of triangular section fitted into compartments defined bymetallic spacing members sup- [56] References Cited ported between apair of steel plates.

UNHED STATES PATENTS 8 Claims, 2 Drawing Figures 1,423,652 H1922EH992!L::- :-:i-v1- p 8.

SAFES AND SIMILAR SECURITY STRUCTURES This invention relates to safesand similar security structures such as strong rooms and is particularlyconcerned with a construction of slab or panel for use either in thedoors or walls of such structures. With the continued improvement insafebreaking equipment it is necessary that corresponding im provementsshould be made in the structures themselves. One of the developments inthis field is the thermic lance which is capable of developing very hightemperatures of the order of 3,000 C. associated with a high level ofheat output in a readily controllable form. Such a device is capable ofburning through any known material but the resultant hole is relativelysmall and it is necessary to burn a ring of such holes before it ispossible to lift out a sufficient portion of a door or wall to gainaccess to the interior of a safe or the structure. If sufficient timeand equipment is available there is no known form of structure which canentirely resist the action of such a device.

According to the present invention a slab or panel for use in a safe orsimilar structure comprises a layer of drill-resisting material which isbacked by a layer of material which melts and vaporizes but does notreact substantially exothermically with oxygen at the high temperaturesinvolved of the order of 3,000 C. as mentioned above. The outer layerprovides the resistance to mechanical attack, which is not necessarilyby drilling, but may be by punching, for example. The termdrillresisting is used for convenience to indicate resistance to anyform of mechanical attack. The effect of the nature of the layer ofbacking material is that, in the oxygen-rich environment provided by athermic lance, the material does not readily burn out but as justmentioned merely melts and vaporizes. This melting and vaporizationinvolves the provision of such large amounts of latent heat that theoperating temperature of the device is maintained only at the expense ofincreased consumption of lance and oxygen. The material is, of course,gradually removed in either a molten or vapor state and a hole willeventually be made right through the slab or panel, but it is found thatthis takes several times as long as it does to make a hole through asimilar thickness of material at present used for such a slab or panel.The speed at which the material is removed is found to depend on anumber of parameters including thermal conductivity, specific heat,latent heat of fusion and of vaporization, melting point and resistanceto thermal shock.

Depending on the particular duty involved and costs consistent with thisduty it is possible to calculate the necessary properties of the idealmaterial on the basis of these factors. In practice the material whichbest meets the majority of operating requirements is graphite butdepending on the circumstances other materials such as tantalum,titanium or zirconium or compounds or mixtures of these elements or ofthe ores in which they naturally occur, having physical propertiesappropriate to the degree of resistance desired, may be used.

The layer of drill-resisting material is preferably in the form ofnuggets of hard material embedded in a ductile metal matrix, e.g.,nuggets of aloxite in a copper matrix. This layer provides the externalprotection against mechanical attack but offers little resistance to theaction of a thermic lance. A hole can therefore be burnt in this outerlayer comparatively rapidly but as soon as the hole extends as far asthe backing layer the penetration is slowed down to a major extent forthe reasons already described. The layer of drill-resisting material is,however, essential so as to protect the front face of the slab or panelfrom mechanical attack. Most simply a single layer of thisdrill-resisting material is backed by a single layer of vaporizablematerial and such a construction is found to be adequate for themajority of applications. Under some circumstances, however, forexample, strong room doors of a greater than usual thickness more thanone double layer may be provided with advantage. For example the doublelayer of drill-resisting material and vaporizing material may merely beduplicated and indeed any required number of such double layers may beprovided. Alternatively intermediate layers of other materials may alsobe included, the only overriding requirement being that the face whichis intended to define the front of the slab or panel is made of a layerof drill-resisting material while at some spacing to the rear of this isat least one layer of vaporizing material.

In a particular construction it may take 10 or 12 times as long topierce a hole through the slab. This not only needs a correspondinglygreater number of then'nic lances together with associated equipmentsuch as oxygen cylinders all of which is difficult to transport to thesite, but the time required for the operation as a whole, i.e., theburning of a sufficient number of holes to obtain access to the interiorof the safe is extended to such an extent that in the majority of casesit may well be unacceptable. In other words, although it is stillpossible eventually to gain access to the interior of the safe the timerequired is so much longer that in the majority of cases the operationas a whole becomes impracticable.

Particularly when graphite is used as the vaporizable material it isconvenient for it to be fitted in the form of blocks which may befabricated by sintering, fusing, casting and so forth. By making theseblocks of a regular cross section they may be fitted together so as toform a virtually continuous layer with relatively small airspaces. Forthis purpose the individual blocks may be fitted into compartments atleast partly defined by metal spacing members. The most convenient crosssection for this purpose is triangular in which case the spacing membersmay be inclined to a plane perpendicular to the surface of the layer ofthe material. This enables the spacing members to perform a secondaryfunction in impeding the burning of a hole through the layer. Since thespacing members are inclined to the direction of a hole which is burntthe heat impinging on a spacing member as soon as the graphite has beenremoved to a sufiicient extent, tends to be conducted away by thespacing member, and owing the the inclination of the latter thedirection of the hole itself tends to be correspondingly diverted. As aresult the hole is forced to penetrate a greater thickness of graphiteand moreover the fact that successive holes do not extend directlythrough the thickness of the slab makes it more difficult to obtain thenecessary accuracy to remove a complete section of the complexconstruction of slab. For this reason it is generally necessary to burna larger number of holes than would otherwise be necessary before thesection as a whole can be removed and this makes the operation as awhole take even longer and entails the consumption of larger quantitiesof lance and oxygen.

A construction of complex slab or panel in accordance with the inventionwill now be described in more detail with reference to the accompanyingdrawings in which:

FIG. 1 is a cross-sectional view, and,

FIG. 2 is a perspective view to a reduced scale illustrating the mannerof assembly.

The composite slab shown in the drawings comprises only a single layerof drill-resisting material and a single layer of vaporizable material.This is found to be adequate for a large number of general applicationsbut as already described it may be desirable to provide a multilayerconstruction comprising a number of the double layer units shown in FIG.1 or alternatively a combination of the individual layers shown in FIG.1 with layers of other material. In FIG. 1 a layer of drill-resistingmaterial is indicated generally as 1 while a layer of vaporizablematerial, graphite in this particular example, is shown as 2. The twolayers are separated by a gap 3 which in the example shown is left emptyto form an airspace. It is, however, possible to fill this gap with someother material to form the kind of multilayer construction referred toabove.

Turning now to the details of the construction the layer 1 comprises acentral portion 4 consisting of nuggets of aloxite in a copper matrix.The size of the nuggets is not critical but in a particular example inwhich the thickness of the copper matrix is approximately an inch and ahalf the average size of the nuggets may be approximately half an inch.The central portion 4 is bonded to a mild steel plate 5 by anglebrackets 6 extending from the surface of the plate. On the front side ofthe layer 4 is a further mild steel plate 8 which is supported bysideplates 9 and 10 so that there is a narrow airgap between the plate 8and the layer 4. The components 4, 5 and 8 together make up a compositedrill-resisting layer.

The layer 2 is made up of blocks 12 of graphite of triangular section asshown, which are preformed and individually inserted into compartmentsdefined by spacing members 13 and by front and backplates 14 and 15.Apart from the two blocks at the ends of the section the remainingblocks are all in the form of isosceles right-angled triangles so thatthe angles at the base of each triangle are 45 and the spacing members13 extend at 45 to the plane perpendicular to the surface of the layer.During assembly the spacing members 13, which may be for example of mildsteel or copper, are first welded to the plate 14 as shown by the welds18. The plate 15 is then fitted subsequently and is secured to theapices of the triangles defined by the spacing members 13 by welds 19made through corresponding holes in the plate 15. The preformed blocksof graphite are then inserted in the compartments thus defined, beingslid in from one end as illustrated in FIG. 2. One end plate, not seenin the drawings, is first welded in position at the bottom as seen inFlG. 2, after which the blocks 12 are slid into position and the upperend plate 20 is fitted in position, being held by means of welds madethrough holes 21 connecting with the plate 5.

if the construction shown in FIG. 1 is acted on by a thermic lance thelayer 1 is penetrated relatively easily. The gap 3 is then encounteredand this allows the heat to spread laterally thus reducing theconcentration of heat on the layer 2. The graphite will, however,eventually be heated to a temperature at which it melts and vaporizesbut owing to the fact that it does not react exothermally with theoxygen present it does not readily burn and therefore is effectivelyremoved only by the melting and vaporizing which as previously mentionedinvolves the provision of large amounts of latent heat. When the holeeventually reaches one of the spacing members 13 the spacing membertends to conduct the heat away so that the hole tends to deflect in thegeneral direction of the spacing member, i.e., at an angle of about 45.This causes the hole to penetrate a greater thickness of graphite sothat a further large quantity of latent heat has to be provided.Eventually, however, the hole will penetrate right through the compositeslab.

A single hole will not, of course, be sufficient for purposes of accessand it is necessary to burn a number of holes before the section as awhole can be removed. Owing to the devious and unpredictable courses ofindividual holes a considerably larger number is required than wouldotherwise be necessary. Difiiculty of access is further increased byappropriate spacing of the welding points 18 of the spacing members 13and it is found that the optimum distance between adjacent points 18 isapproximately eight inches. This figure is independent of the otherdimensions and is arrived at since it ensures that even when sufficientholes have been pierced to span the width of a complete block 12 andmaterial in this region has been removed there is still not sufficientspace for the entry of a tool to work further on the spacing members,particularly in view of the need to approach them via a suitable hole inthe outer layer of drill-resisting material 1. Any spacing appreciableless than eight inches might enable complete section to be cut out moreeasily and an appreciably wider spacing might accommodate a handholeentirely within the width of one block. For this combination of reasonsa spacing of eight inches is the optimum value.

We claim:

1. A safe having at least one wall including a slab comprising acontinuous face layer, said face layer being of drill-resisting materialand comprising nuggets having at least the hardness of fused aluminaembedded in a ductile metal matrix, a backing layer of material whichmelts and vaporizes but does not substantially react exothermically withoxygen at temperatures of the order of 3,000 C., and means additional tosaid face layer for supporting said backing layer behind said face laer.

2. A slab according to claim 1, comprising a single layer ofdrill-resisting material and a single layer of vaporizable material.

3. A slab according to claim 1 in which said vaporizable material isgraphite.

4. A slab according to claim 1 in which said face layer comprises aductile metal matrix and nuggets of hard material in said metal matrix.

5. A safe having at least one wall including a slab comprising acontinuous face layer, said face layer being of drill-resistingmaterial, and a backing layer, said backing layer including metallicspacing members defining at least in part a plurality of compartments ofregular cross section, and a plurality of bars of a material which meltsand vaporizes but does not substantially react exothermically withoxygen at temperatures of the order of 3,000 C., said bars being ofcorresponding cross section to said compartments and being located insaid compartments.

6. A slab according to claim 5, in which said blocks are of triangularcross section and said spacing members are inclined to a planeperpendicular to the surface of said backing layer.

7. A slab according to claim 6, including a pair of steel plates formingthe outer sides of said compartments, said spacing members beingsupported by said plates.

8. A slab according to claim 7 in which said spacing members are securedto said steel plates at a spacing of approximately eight inches.

1. A safe having at least one wall including a slab comprising acontinuous face layer, said face layer being of drill-resisting materialand comprising nuggets having at least the hardness of fused aluminaembedded in a ductile metal matrix, a backing layer of material whichmelts and vaporizes but does not substantially react exothermically withoxygen at temperatures of the order of 3,000* C., and means additionalto said face layer for supporting said backing layer behind said facelayer.
 2. A slab according to claim 1, comprising a single layer ofdrill-resisting material and a single layer of vaporizable material. 3.A slab according to claim 1 in which said vaporizable material isgraphite.
 4. A slab according to claim 1 in which said face layercomprises a ductile metal matrix and nuggets of hard material in saidmetal matrix.
 5. A safe having at least one wall including a slabcomprising a continuous face layer, said face layer being ofdrill-resisting material, and a backing layer, said backing layerincluding metallic spacing members defining at least in part a pluralityof compartments of regular cross section, and a plurality of bars of amaterial which melts and vaporizes but does not substantially reactexothermically with oxygen at temperatures of the order of 3,000* C.,said bars being of corresponding cross section to said compartments andbeing located in said compartments.
 6. A slab according to claim 5, inwhich said blocks are of triangular cross section and said spacingmembers are inclined to a plane perpendicular to the surface of saidbacking layer.
 7. A slab according to claim 6, including a pair of steelplates forming the outer sides of said compartments, said spacingmembers being supported by said plates.
 8. A slab according to claim 7in which said spacing members are securEd to said steel plates at aspacing of approximately eight inches.